An energy absorption apparatus is known to be utilized on a railroad car in various applications and between two masses. For example, an energy absorption apparatus is typically arranged in operable combination with a railroad car draft gear for absorbing forces between adjacent ends of railroad cars. A railroad car energy absorption apparatus is also commonly configured as a side bearing. A railroad car side bearing is typically disposed to opposite sides of a car body between a centerpiece or bolster of a wheeled truck and an underside of the railroad car body. During movement of the railcar, each side bearing acts as an energy absorption apparatus and furthermore serves to control or restrict “hunting” movements of the railcar.
Hunting is a phenomenon created by the wheeled trucks during movement of the railway vehicle over tracks or rails. The coned wheels of each truck travel a sinuous path along a tangent or straight track as they continually seek a centered position under the steering influence of wheel conicity. In traveling such a sinuous path, a truck will yaw cyclically in an unstable fashion with respect to the car body about an axis defined by a vertical centerline of the truck bolster. Hunting, and the resulting side or lateral translation or oscillation of the railway car body is of particular significance when the car is traveling in an empty condition at relatively high speeds, e.g., in excess of 45 miles per hour. Of course, the truck also tends to yaw or rotate quasi-statically with respect to the car body in negotiating curved sections of track. Suffice it to say, excessive hunting can result in premature wear of the wheeled truck components including the wheels. Hunting can also cause damage to lading being transported in the railroad car body.
Known railroad car energy absorption devices typically use compressed resilient members such as spring loaded steel elements or elastomeric blocks or columns or both. The spring loaded steel elements, utilizing a steel on steel friction interface, proved ineffective in some applications because of seizing and galling problems. Recently different forms of thermoplastic elastomers have advantageously been used to develop the necessary force absorption characteristics required for such railroad car uses. One such elastomer is marketed and sold by the Assignee of the present invention under the tradename “TecsPak”.
Regardless of the application, the buildup of heat in proximity to the thermoplastic spring is a serious concern. During operation of the railroad car and use of such energy absorption apparatus, heat develops. Unless such heat buildup can be controlled, however, the thermoplastic spring will tend to soften and deform, thus, adversely affecting the operable performance of the railroad component with which it finds utility. For example, as a wheeled truck yaws back and forth, an undersurface of the railcar body slides across and relative to a metal top plate of the side bearing which is biased against the undersurface of the railcar body by the elastomeric spring. The resulting friction advantageously produces an opposite torque which acts to inhibit yaw motion. Such resulting friction also typically causes an excessive amount of heat at the interface between the top plate and the underside of the car body. Such heat buildup often exceeds the heat deflection temperature of the thermoplastic spring. As used herein and throughout, the term “heat deflection temperature” means and refers to a temperature level at which the related component, regardless of its composition, tends to soften and deform.
When such localized heat created by the friction between the side bearing and the car body exceeds its heat deflection temperature, the elastomeric spring will tend to deform and/or, when the temperature is high enough, cause melting of the elastomeric spring. Deformation and melting of the elastomeric spring significantly reduces the ability of the spring to apply a proper preload force and, thus, decreases vertical suspension characteristics of the side bearing which, in turn, results in enhanced hunting of the wheeled truck. Enhanced hunting and/or unstable cyclic yawing of the truck increases the resultant lateral translation/oscillation of the railcar leading to a further increase in the levels of heat buildup and further deterioration of the elastomeric spring.
Thus, there is a need and continuing desire for a railroad car energy absorption apparatus having a spring assembly including an elastomeric spring arranged in operable combination with structure for inhibiting deterioration of the elastomeric spring resulting from localized heat.